linux-kernel - Re: [PATCH 3/5] mm/vmalloc: Initialize VA's list node after unlink

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Date:   Thu, 9 Jun 2022 15:53:26 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 3/5] mm/vmalloc: Initialize VA's list node after unlink

On Thu, Jun 9, 2022 at 3:30 PM Baoquan He <bhe@...hat.com> wrote:
>
> On 06/09/22 at 02:36pm, Uladzislau Rezki wrote:
> > >
> > > On 06/07/22 at 11:34am, Uladzislau Rezki (Sony) wrote:
> > > > A vmap_area can travel between different places. For example
> > > > attached/detached to/from different rb-trees. In order to
> > > > prevent fancy bugs, initialize a VA's list node after it is
> > > > removed from the list, so it pairs with VA's rb_node which
> > > > is also initialized.
> > > >
> > > > There is no functional change as a result of this patch.
> > > >
> > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > > ---
> > > >  mm/vmalloc.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index 745e89eb6ca1..82771e555273 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -978,7 +978,7 @@ __unlink_va(struct vmap_area *va, struct rb_root *root, bool augment)
> > > >       else
> > > >               rb_erase(&va->rb_node, root);
> > > >
> > > > -     list_del(&va->list);
> > > > +     list_del_init(&va->list);
> > >
> > > Don't object this change, while list_del poison members, which is also
> > > not bad?
> > >
> > It is not bad for sure. The main aim was to be align with what the
> > RB_CLEAR_NODE() does, i.e. initialize VA when it is detached
> > and be safe with list manipulation when it is detached. For example
> > whether it is empty or not: list_empty(), etc.
>
> Agree. list_del() can't make list_empty() work, and RB_CLEAR_NODE() has
> done the clearing already.
>
> Then this change looks reasonable to me, thanks.
>
> Reviewed-by: Baoquan He <bhe@...hat.com>
>
Thanks!

-- 
Uladzislau Rezki